This invention relates to an automatic welding apparatus, and more particularly to improvements in a stationary torch type automatic fillet-welding apparatus for forming a circular bead along the circumference of a tubular or cylindrical first workpiece at its junction with respect to a substantially flat second workpiece in order to weld the former to the latter.
The automatic fillet-welding apparatus for forming a circular bead is utilized, for example, in the manufacture of construction machines such as a power shovel, in order to weld a tubular member such as a boss (first workpiece) to a substantially flat-shaped arm or a plate (second workpiece).
The conventional automatic fillet-welding apparatus for forming a circular bead may be roughly classified into two types, that is, a stationary torch type and a movable torch type.
A typical model of the stationary torch type is disclosed, for example, in a catalog as of Oct. 1, 1982 published by Welding Equipment Department of Matsushita Electric Industrial Co., Ltd., Osaka, Japan. More particularly, on Page 2 of the catalog, there is disclosed a typical stationary torch type automatic circular arc welding apparatus named "PANATURN S" (Model YJ-1013E-3). Another typical model of the stationary torch type is also disclosed in U.S. Pat. No. 4,014,495 to Oda et al. The stationary type circular fillet-welding apparatus is generally provided with a fixed welding torch and a turntable on which a second workpiece, having a first workpiece provisionally fixed thereto, is clamped in position, wherein a desired circular fillet-welding is performed during one rotation of the turntable.
A typical model of the movable torch type is disclosed, for example, in U.S. Pat. No. 3,439,856 to E. J. Philipps et al, wherein a welding torch is arranged so as to move round a tubular first workpiece fixed in position.
The movable torch type apparatus generally has such disadvantages that a welding cable connected to a welding torch is occasionally twisted during turning movement of the torch and that troublesome or time-consuming preparation is required for accurately adjusting a turning radius of the torch in accordance with a radius of a tubular first workpiece to be welded to a flat second workpiece. However, such disadvantages of the movable torch type are not observed in the stationary torch type apparatus. However, the conventional stationary torch type apparatus has its own disadvantages.
Since the present invention is directed to improvements in the stationary torch type automatic fillet-welding apparatus for forming a circular bead, detailed description will now be made hereinafter in connection with FIG. 7 of the accompanying drawings in order to clarify the general structure of the same type of the conventional apparatus and the inherent disadvantages invited by the particular structure thereof.
In FIG. 7, there is illustrated a typical example of the conventional stationary torch type automatic circular fillet-welding apparatus as having a turntable 1 inclined at an angle of 45.degree. with respect to a horizontal plane and rotatably supported by a machine frame 2 in which a known drive mechanism is housed. The turntable has a plurality of known spaced T-slots formed in its outer surface wall, so that clamp members 3 can be engaged with the slots with the aid of known T-slot bolts and nuts, conventionally.
In preparation, a tubular first workpiece 7 is provisionally fixed in position to a flat second workpiece 4 for example by tack-welding. The second workpiece 4 is fixed in position to the turntable 1 by means of the clamp members 3 which are engaged with the T-slot bolts and nuts as illustrated. It is to be noted that the first tubular workpiece 7 on the second workpiece 4 should be positionally adjusted so that its center is accurately coincident with the center of the turntable 1.
A welding torch 5 supported by a supporter 6 is adjustably positioned so that its working end is exactly directed to the junction of the first and the second workpieces 7 and 4. Thus, as the turntable 1 rotates about its center, a desired circular fillet-welding is carried out by the fixed welding torch 5 to weld the first tubular workpiece 7 to the second flat workpiece 4 at the circular junction of the workpieces 7 and 4. In this connection, it will be easily understood that, because the turntable 1 is inclined at an angle of 45.degree. with respect to a horizontal plane, a formed weld bead is equally distributed to both sides of the workpieces 4 and 7.
Because of the above described particular structure of the conventional stationary torch type apparatus, the center of the first tubular workpiece 7, provisionally fixed to the flat second workpiece 4, should be exactly coincident with the center of the turntable 1, resulting in that troublesome and time-consuming preparation is inevitably required for adjusting the center of the first workpiece 7 to the center of the turntable 1. More particularly, because a part of the second workpiece 4 is inevitably placed over the center of the turntable 1, this center is inevitably hidden by the second workpiece 4, resulting in that an operator cannot find an accurate location of the center of the turntable 1 with his eyes and thus it is necessary to rely upon troublesome measurements to find the location. This preparation is especially troublesome and time-consuming in the case where the workpieces 4, and 7 are large in size.
Further, in the case where it is necessary to weld two or more tubular first workpieces 7 to a flat second workpiece 4, as illustrated in FIG. 7, the second workpiece 4 must be moved each time after one circular welding operation is over, which is very inefficient. Furthermore, in the case where a first workpiece 7 is welded to one extremity of a considerably long-sized second workpiece 4, a turning radius of the workpiece 4 becomes so large that the overhanging portion (portion which radially extends beyond the circumference of the turntable) of the workpiece 4 may collide with the ground or any other thing lying in the vicinity during operation, which is very dangerous.
It is, therefore, an object of the invention to substantially reduce the above-discussed disadvantages in the conventional stationary torch type automatic circular fillet-welding apparatus.
Another object of the invention is to provide an improved stationary torch type automatic circular fillet-welding apparatus in which it is no longer necessary to positionally adjust the center of a tubular or cylindrical first workpiece, provisionally fixed to a flat second workpiece, to the center of a turntable.
A further object of the invention is to provide an improved stationary torch type automatic circular fillet-welding apparatus which permits welding of a plurality of tubular or cylindrical first workpieces to a substantially flat-shaped second workpiece one after another without moving the second workpiece which has been fixedly clamped to the turntable.
A still further object of the invention is to provide an improved stationary torch type automatic circular fillet-welding apparatus in which a flat-shaped second workpiece may be clamped at any desired position of the turntable, so that a length of a overhanging portion of the long-sized second workpiece can be minimized.
Other objects, features and advantages of the invention will become apparent from the detailed description given hereinafter in connection with the accompanying drawings.
According to the present invention, there is provided a stationary torch type automatic circular fillet-welding apparatus including a stationary welding torch, an inclined turntable to which a substantially flat-shaped second workpiece is clamped, a torch holder and a torch positioner which cooperate with each other to always maintain a working end of the welding torch in such a preset constant position radially spaced apart by a predetermined distance from the center of a tubular or cylindrical first workpiece provisionally fixed to the second workpiece, and a positioner guide mechanism for guiding the torch positioner to any desired position in such a particular plane that extends in parallel relationship with respect to a surface plane of the turntable. The torch positioner is supported by the positioner guide mechanism in such a manner that the former is restricted from rotation on its own axis by the latter.